This invention relates to a thermal image sensor that utilises a liquid crystal layer as the sensor element.
One example of such a sensor employs a cholesteric layer the pitch of whose helix is particularly strongly temperature dependent. Such a layer is thermostatted to a carefully controlled temperature such that the radiation of a thermal image imaged upon it produces local variations in pitch to produce a thermochromic effect. One of the limitations of this approach to thermal image sensing is that the sensitivity is predetermined by the choice of the cholesteric material. Another limitation is that not only does there have to be a high degree of uniformity of the temperature of the layer over the whole image area before exposure to the radiation of the thermal image, but also the absolute value of that temperature needs to be held within relatively narrow limits.